A method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention comprises the steps of: hot-rolling a slab to prepare a hot-rolled sheet, the slab containing, in wt %, 2.0 to 6.0% of Si, 0.04 to 0.12% of Mn, 0.001 to 0.022% of N, 0.027 to 0.060% of C, 0.01 to 0.08% of Nb, 0.01% or less of Ti, and the balance of Fe and other inevitable impurities; cold-rolling the hot-rolled sheet to prepare a cold-rolled sheet; and subjecting the primarily recrystallization-annealed cold-rolled sheet to secondary recrystallization annealing.

An exemplary embodiment in the present disclosure provides a grain-oriented electrical steel sheet containing, by wt %: 3.0 to 4.5% of Si; 0.05 to 0.2% of Mn; 0.015 to 0.035% of Al; 0.0015% or less (excluding 0%) of C; 0.0015% or less (excluding 0%) of N; 0.0015% or less (excluding 0%) of S; and a balance of Fe and other unavoidable impurities, wherein the grain-oriented electrical steel sheet satisfies the following Relational Expressions 1 and 2:

(W.sub.13/50/W.sub.17/50)≤0.57  [Relational Expression 1]

(W.sub.15/50/W.sub.17/50)≤0.76  [Relational Expression 2] where Wx/y represents a core loss value under conditions in which a magnitude of an applied magnetic field is x/10 T and a frequency is y Hz.

An exemplary embodiment in the present disclosure provides a grain-oriented electrical steel sheet containing, by wt %: 3.0 to 4.5% of Si; 0.05 to 0.2% of Mn; 0.015 to 0.035% of Al; 0.0015% or less (excluding 0%) of C; 0.0015% or less (excluding 0%) of N; 0.0015% or less (excluding 0%) of S; and a balance of Fe and other unavoidable impurities, wherein the grain-oriented electrical steel sheet satisfies the following Relational Expressions 1 and 2:

(W.sub.13/50/W.sub.17/50)≤0.57  [Relational Expression 1]

(W.sub.15/50/W.sub.17/50)≤0.76  [Relational Expression 2] where Wx/y represents a core loss value under conditions in which a magnitude of an applied magnetic field is x/10 T and a frequency is y Hz.

Provided is a steel sheet having properties particularly suitable as a material of automotive external panels because bake hardenability and room-temperature aging resistance are excellent, and a method of manufacturing the steel sheet.

Provided herein is a high-strength seamless steel pipe, and a method for manufacturing same. A high-strength seamless steel pipe of the present invention has a steel microstructure with a prior austenite grain size of 11.0 or more in terms of a grain size number in compliance with ASTM E112, and has a yield strength of 862 MPa or more and 965 MPa or less.

A steel sheet has a predetermined chemical composition containing, in mass %, C: more than 0.18% and less than 0.30%, Mn: more than 2.50% and 4.00% or less, and other elements. The steel micro-structure at a position at a depth of ¼ of the sheet thickness from the surface in an L cross section of the steel sheet is, in area %, tempered martensite: 25 to 90%, ferrite: 5% or less, retained austenite: 10 to 50%, and bainite: 5% or less. At a position at a depth of ¼ of the sheet thickness from the surface of the L cross section, the proportion of a total area of retained austenite grains having an area of 1 μm.sup.2 or more and having a grain shape circularity of 0.1 or more is less than 50% with respect to the entire area of retained austenite. The steel sheet satisfies the formula C.sub.Mnγ/C.sub.Mnα≥1.2.

Methods and systems for additively casting of a metallic object include constructing a mold region of a current production layer before producing the object region of the current production layer; depositing molten metal at a predetermined temperature in working areas at the object region of the current production layer according to a building plan; and moving one or more heaters over the deposition path and heating the working areas. The heating includes (1) heating the working areas to a pre-deposition target temperature before depositing metal on the working areas to affect a bonding of the molten metal with the working areas, and/or (2) heating the working areas to a post-deposition target temperature after depositing metal on the working areas to affect a thermal cooling profile of the working areas. the heating also includes providing annealing heating to earlier production layers by heat conduction through the current production layer.

Methods and systems for additively casting of a metallic object include constructing a mold region of a current production layer before producing the object region of the current production layer; depositing molten metal at a predetermined temperature in working areas at the object region of the current production layer according to a building plan; and moving one or more heaters over the deposition path and heating the working areas. The heating includes (1) heating the working areas to a pre-deposition target temperature before depositing metal on the working areas to affect a bonding of the molten metal with the working areas, and/or (2) heating the working areas to a post-deposition target temperature after depositing metal on the working areas to affect a thermal cooling profile of the working areas. the heating also includes providing annealing heating to earlier production layers by heat conduction through the current production layer.

Disclosed in the present disclosure is an ultrahigh-strength dual-phase steel. The matrix structure of the ultrahigh-strength dual-phase steel is ferrite and martensite, wherein the ferrite and the martensite are evenly distributed in an island shape. The ultrahigh-strength dual-phase steel contains the following chemical elements in percentage by mass: 0.12-0.2% of C, 0.5-1.0% of Si, 2.5-3.0% of Mn, 0.02-0.05% of Al, 0.02-0.05% of Nb, 0.02-0.05% of Ti, and 0.001-0.003% of B. Further disclosed in the present disclosure is a manufacturing method for the ultrahigh-strength dual-phase steel, comprising the steps of smelting and continuous casting, hot rolling, cold rolling, annealing, tempering, and leveling. The ultrahigh-strength dual-phase steel in the present disclosure has not only good mechanical properties but also excellent delayed cracking resistance and low initial hydrogen content, and can be suitable for manufacturing of vehicle safety structural parts.

Disclosed is a stainless steel for a fuel cell separator, more specifically, a stainless steel for a fuel cell separator having a low contact resistance. According to an embodiment of the stainless steel for a fuel cell separator disclosed herein, an arithmetic mean summit curvature Ssc of the surface defined according to the ISO 25178 standard is at least 6.0 μm.sup.−1, a root mean square surface slope Sdq is at least 23, and a contact resistance is at most 10 mΩ.Math.cm.sup.2.